In a case-control study, selecting controls from the same population primarily reduces which bias?

• A. Recall bias
• B. Selection bias
• C. Publication bias
• D. Measurement bias

Answer: (B)

Choosing controls from the same source population as the cases reduces selection bias. In a case-control study, you compare exposure between those with the disease and those without. If controls come from a different population, their exposure pattern may differ for reasons unrelated to the disease, biasing the estimated association. By selecting controls from the same population that produced the cases, the exposure distribution among controls more accurately reflects what would have been observed in that population if disease had not occurred, making the comparison valid.

Recall bias involves cases and controls recalling past exposures differently, which is not resolved by how controls are selected. Publication bias concerns whether studies with certain results are more likely to be published, not a flaw addressed by control selection. Measurement bias arises from errors in measuring exposure or outcome, which is separate from how controls are drawn.